Radioactive ray detectors including casing constructed to facilitate repair and circuitry for controlling on-off signal



Aprll l, 1969 T. J. RADCLIFFE ET AL 3,436,543

RADIOACTIVE RAY DETECTORS INCLUDING CASING CONSTRUCTED TO FACILITATE REPAIR AND CIRCUITRY FOR CONTROLLING ON-OFF SIGNAL Original Filed Sept. 12, 1961 Sheet of 2 l-l-Ll-L I I INVENTORS THOMAS J. RADQLIFFE o i BY DANIEL M. McELHANEY,JR. DANH-IL F. HAVEL UATTORNEY 3,436,543 RADIOACTIVE RAY DETECTORS INCLUDING CASING CONSTRUCTED TO FACILITATE REPAIR AND CIRCUITRY FOR CONTROL- LING ON-OFF SIGNAL Thomas J. Radclifie, Warrensville Heights, Daniel M.

McElhaney, Jr., Euclid, and Daniel F. Havel, Cleveland, Ohio, assignors to Republic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Original application Sept. 12, 1961, Ser. No. 137,588, now Patent No. 3,304,241, dated Feb. 14, 1967. Divided and this application July 7, 1966, Ser. No. 563,426

Int. Cl. G01t 1/18 US. 'Cl. 250-836 4 Claims ABSTRACT OF THE DISCLOSURE Radioactive ray detector including first casing for wall mounting including on-oif signal, and second casing attachable to first by electrical connector. Detector tube and circuitry located in second casing to facilitate repair of unit by replacement of second casing.

Circuitry includes monostable multivibrator controlled by detector tube and feeding an integrator, whose output is amplified and supplied to ON OlFF signal. Relationship of amplifier output to multivibrator output is such that intermittent reception of rays result in steady actuation of ray indicating signal.

This is a division of our copending application Ser. No. 137,5 88, filed Sept. 12, 1961, entitled Safety Control Apparatus for Coke Oven Batteries, now Patent No. 3,304,241, dated Feb. 14, 1967. That copending application discloses a coke oven battery including safety control apparatus by which information is conveyed between spaced points through smoke or vapor by means of a beam of radioactive rays. In one embodiment, the beam may be turned on and off by means of a shutter at the source. The shutter position is controlled in accordance with various safety devices whose condition it is desired to communicate to the location of the beam detector.

In another modification, the beam source is mounted on a vehicle, and the impingement of the beam on the detector is utilized to determine the presence or absence of the vehicle at a predetermined point.

The present invention relates to detectors of radioactive beams, and particularly to apparatus for operating an electrical relay in accordance with the presence or absence of such beams.

An object of the invention is to provide improved radioactive beam detecting apparatus.

A further object is to provide an improved structure for the radiation detection unit including improved means for mounting it in relation to a window.

Another object is to provide improved electrical circuitry for operating a relay in response to the detection of a radioactive beam.

The foregoing and other objects are attained in the apparatus described herein. The detector unit is mounted in a window through which the beam of rays to be detected may pass. Geiger tubes which form the sensitive element of the detector are located in a cylinder which extends downwardly from the top of the window frame. The detector unit is of modular construction. That is to say, the cylindrical housing containing the Geiger tubes may be separated as a unit from the indicator box unit from which it depends.

The circuit actuated by the Geiger tubes includes a monostable multivibrator which initiates an elongated output pulse each time that a ray impinges on a Geiger tube. The output of the monostable multivibrator is fed to an J United States Patent ice integrator whose output is amplifier and used to control a relay. The circuit components are selected so that the relay is energized in response to a relatively low level of radiation. The relay controls a signal and an interlocking contact in a control circuit.

'In the drawings:

FIG. 1 is an elevational view taken from inside the window, showing the radiation detector unit;

FIG. 2 is a view partly in section and partly in elevation, showing the interior of the radiation detector unit; and

FIG. 3 is a wiring diagram of the circuit of the radiation detector unit.

FIG. 1 is a fragmentary view looking out through a window 57, which may be the control cab of a pusher car associated with a coke oven battery. Above the window 57, on the inside of the wall 58, is mounted an indicator box 59. Depending from the bottom of the indicator box 59 is a cylindrical casing 60 which encloses a plurality of Geiger tubes 61 which constitute the sensitive parts of the detector unit, and other circuit elements associated with those tubes.

FIG. 2 illustrates the indicator box '59 and the casing 60 of FIG. 1 with the cover of the indicator box open and the cylinder 60 cut away to reveal the internal details.

The detector unit 62 inside the cylinder 60 is mounted on a frame consisting of a plurality of through bolts 63 which connect the top and bottom end plates 64. A plurality of spaced plates 65 are mounted on the through bolts 63 at intervals along the length of those bolts. The plates 65 and the bottom end plate 64 support some of the circuit elements, and others are attached to sheets 66 of insulating material fastened to the through bolts 63 by any suitable means. The Geiger tubes 61 are located between the two bottom sets of spacer plates 65.

The length of the detector unit 62 is selected so as to bring the Geiger tubes 61 to a locality just above the top of a pusher ram 12 (see FIG. 1). Although it is necessary to bring the Geiger tubes 61 into alignment with the path of the radioactive beam, it is desired to extend the casing 60 and unit 62 downwardly no further than necessary, so as to minimize the obstruction to the view through the window The elements mounted on the frame 62 are connected by wires (for the most part omitted from FIG. 2) which extend through a plug connector 67 to the circuit elements inside the indicator box 59.

Mounted in the indicator box and visible from the outside thereof to the operator of the pusher car are a signal lamp 68 whose illumination indicates that the radioactive beam is being detected, a power on signal lamp 69, a fuse blown signal lamp 70 and a meter 71 which indicates the intensity of the radiation detected by the unit.

The cylinder '60 is provided on its outer surface near its upper end with a projecting flange 72 adapted to seat against a seating ring 73 which is welded or otherwise suitably fastened to the bottom of the indicator box 59. The seating ring 73 is externally threaded and is adapted to receive the internal thread on a retainer ring 74 having an inwardly projecting flange at its lower end adapted to engage and hold in place the flange 72 on the cylinder 60.

The cylinder 60 may be removed by first removing the retainer ring 74, without disturbing the elements on the frame 62 inside the cylinder 60. Furthermore, after the cylinder 60 has been removed, the entire detector unit 62 can be removed simply by separating the plug 67. In the event of failure of the detector unit for any reason, it can be readily and quickly replaced by a new detector unit. The units in the indicator box 59 are preferably also of plug-in construction, to facilitate repair and replacement.

FIG. 3 is a wiring diagram showing (1) the electrical control circuits for a pusher drive motor which operates the pusher ram 12, (2) the circuits in the indicator box 59, and (3) the circuits in the detector unit 62. This figure also illustrates graphically the wave forms at certain points in the detector unit 62.

Referring to FIG. 3, there are shown power supply lines and 76. A motor 79 for driving the pusher 12 includes an armature 77 and a field winding 78. The motor windings are illustrated as for a DC series motor. It will be readily understood that shunt or compound motors may be used. A series motor is selected simply for purposes of illustration. The motor 79 is controlled by a forward push button and a reverese push button 81. Push buttons are shown for the purpose of simplifying the diagram. It will be readily understood that other conventional controllers and starting boxes may be employed. Energization of the motor 79 is also controlled by a reversing relay 82 having contacts 82a and 82b and an interlocking relay 83 having a contact 83a. When the forward push button 80 is depressed, a circuit is completed for energizing the reversing relay 82, and another circuit is completed for energizing the motor 79, but the latter circuit is completed only if the interlocking relay 83 is energized. The interlocking relay 83 may be energized by the circuits to be described below, in response to the simultaneous occurrence of several related events, including the impingement of the beam 29 of radioactive rays on the Geiger tubes 61. Alternatively, the interlocking relay 83 may be energized by depressing a bypass push buttcn 84.

The circuit for energizing the reversing relay 82 may be traced from positive power supply line 75 through push button 80, wire and relay winding 82 to the negative power supply line 76. When push button 80 is depressed, the circuit just traced for energizing reversing relay 82 is completed, along with a circuit for energizing motor 79 in the forward or coke pushing direction. The circuit for motor 79 may be traced from positive power supply line 75 through push button 80, wire 86, armature 77 of motor 79, contact 83a of interlocking relay 83, contact 82b of relay 82, now closed on its upper stationary contact wire 87, motor field winding 78, wire 88, contact 82a of relay 82, now closed on its upper stationary contact, thence to the negative power supply line 76. Note that in this circuit the right-hand terminal of the field winding 78 is connected to the negative power supply line 76.

When the reverse push button 81 is depressed, the circuit for reversing relay 82 is not completed. A circuit is completed for energizing motor 79 to drive the pusher in the reverse or retracting direction. This circuit does not require the energizing of interlocking relay 83. This circuit for motor 79 may be traced from power supply line 75 through push button 81, armature winding 77, wire 89, the contact 82a of relay 82, now closed on its lower stationary contact, wire 88, field winding 78, wire 87, contact 82b now closed on its lower stationary contact and thence to the negative power supply line 76. Note that this circuit, the left-hand terminal of field winding 78 is connected to the negative power supply line 76, so that the motor 79 runs in the opposite direction from that produced by closure of the push button 80.

Three circuits (in addition to the emergency push button 84) are provided for energizing the interlocking relay 83. One of these circuits may be traced from positive power supply line 75 through wire 90, a switch 91 operated by a cam driven by motor 79, a contact 92a of a relay 92, wire 93, relay winding 83, and thence to the negative power supply line 76.

The switch 91 is closed when the pusher is in its retracted position and remains closed until the pusher moves forward to a position where it is abutting the coke face just inside an open oven. This circuit allows the operator to run the pusher forward to the coke face without waiting for energization of the signal rail 9 by the operators or apparatus on the coke side of the oven. The coke may thereby be prevented from spilling out the open door on the pusher side of the oven while waiting for preparations for the pushing operation to be completed on the coke side of the oven. If desired, the contact 92a may be omitted from the circuit just traced, the switch 91 being then directly connected to the wire 93. In that event, the pusher car o erator does not have to wait for energization of relay 92 to move the pusher up to the coke face.

The second circuit for energizing interlocking relay 83 may be traced from signal rail 9 through a wire 148, contact 92b of relay 92, Wire 93, relay winding 83 and thence to negative power supply line 76. This circuit, which is the one normally used for energizing relay 83, requires positive energization of signal rail 9 and energization of relay 92.

The third circuit for energizing relay 83 may be traced from signal rail 9 through a switch movable between an open position shown in full lines in the drawing and marked by the legend automatic and a closed position shown in dotted lines in the drawing and marked with the legend manual, and thence through wire 93 and winding 83 to negative power supply line 76. The switch 95 is normally kept in the automatic position shown, and is moved to the manual position only in the case of power failure or some other malfunction of the radiant energy detector 62, which would prevent relay 92 from being energized. When the switch 95 is in its manual position, the pusher may be driven forward whenever the signal rail is energized by the operators or apparatus on the coke side of the oven.

Relay 92 is a relatively heavy duty power relay and is controlled by a sensitive relay 94, whose energization is determined by the detector unit 62. The energizing circuit for relay 92 may be traced from positive power supply line 75 through one pole of a double pole switch 96, a fuse 97, detector unit power line 98, wire 99, the single contact of relay 94 and thence through the winding of relay 92 and the other pole of double pole switch 96 to the negative supply line 76.

The power relay 92, the manual-automatic switch 95, and the power control switch 96 may all be conveniently located in a single control unit 100, located separately from the indicator box 59 and the detector unit 62. The switch 96 is used to cut off power from the indicator box 59 and detector unit 62 whenever it is necessary to make repairs on those units. A current limiting resistor 107 is placed in the control unit 100 because of the possible high power dissipation by that resistor, which might overheat some of the elements in the box 59 on the detector unit 62.

The indicator box 59 includes the pusher and guide aligned signal 68, the fuse blown signal 70 and the power on signal 69, previously mentioned, together with the meter 71 and relay 94. The indicator box 59 also includes two diodes 101 and 102, a fuse 103, and current limiting resistors 104, 105 and 106. The indicator box 59 also includes a pair of Zener diodes 108, 109 connected in series.

The relay 92, its contacts, and the signal lamp 68 may each be regarded as a control element shiftable between an inactive condition (deenergization of winding of relay 92, open contacts, dark lamp) indicative that the alignment of the guides and the pusher with the oven has not been communicated to the control element (although that alignment may nevertheless exist) and an active condition (energization of relay 92, closed contacts, illuminated lamp) indicative that the alignment of the guides and the pusher has been communicated to the control element. Hence, the term control element as used in this specification is intended as a generic term inclusive of a member (e.g., contact 92a) movable between an inactive position and an active position and an electrical device (e.g., lamp 68) shiftable between an inactive deenergized condition and an active energized condition. In all cases, the inactive condition is readily and sharply distinguishable from the active condition, as is necessary for safety.

Diodes 101 and 102 are provided primarily to protect the detector from line transients. The provision of the diodes 101 and 102 and resistor 106 allow the circuit to be used on either a power supply at 250 volts DC, as shown, or on 125 volts A.C., a common power supply voltage which may be encountered in some installations. While a 250 volt DC. power supply is common in most steel mills and hence in coke oven batteries, the detector illustrated is useful in other control systems, where the more common 125 volt A.C. supply may be the only supply available.

The positive power supply line may be traced from wire 98 through diode 101, fuse 103, wire 110, and current limiting resistor 107 to a line 111 which extends to the detector unit 62. Similarly, the negative supply line may be traced from the left-hand pole of switch 96 through a wire 112, diode 102 and resistor 106 to a power supply line 113 which extends to the detector unit 62.

The Zener diodes 108 and 109 are connected in series between the lines 111 and 113 and regulate the potential supplied to the detector unit 62.

The fuse blown indicator lamp 70 is connected across the fuse 103 and is illuminated if the fuse 103 blows out. A capacitor 114 is connected between the power input side of fuse 103 and the wire 113 to bypass high frequency transients which may be picked up in the power lines. The power on indicator lamps 69 are connected in parallel and in series with the resistor 105 across the power supply lines to indicate positively that power is being supplied to the detector 62.

The pusher aligned signal lamp 68 is connected in a circuit which may be traced from the positive power supply line through resistor 104, lamp 68, contact 92c of relay 92 to the negative power supply line. The lamp 68 is energized whenever the relay 92 is energized.

Relay winding 94 is connected between the positive power line 111 and an output line 115, whose potential is controlled by the detector 62. Meter 71 is connected in series with a resistor 116 and the series group consisting of meter 71 and resistor 116 is connected in parallel with relay winding 94. A diode 116a is also connected in parallel with relay winding 94.

The detector unit 62 includes the Geiger tubes 61, shown 'as being five in number, although the particular number used is not critical. Also included in the detector unit 62 is a high voltage power supply circuit for the Geiger tubes. That circuit includes a transistor 117, atransformer 118 and a half-wave rectifier diode 119. The output signals from the Geiger tubes 61 are supplied to a monostable multivibrator including transistors 120 and 121. The output of the multivibrator is fed to an integrating circuit including a diode 122 and a capacitor 123. The potential across the capacitor 123 of the integrating circuit is supplied to the input of a transistor 124 connected as an amplifier, whose output is supplied to the relay 94 and the meter 71 in parallel with that relay. Diode 116a protects transistor 124 from transients which might occur when relay 94 is energized.

The power supply circuit for the Geiger tubes 61 includes a resistor 125 having its right-hand terminal connected to the positive supply line 111 and its left-hand terminal connected through a wire 126 to a center tap on the primary winding of a. transformer 118. The wire 126 is also connected through a resistor 127 to the base electrode of transistor 117. The emitter of transistor 117 is connected to line 113, which is in turn connected to ground through a bypass capacitor 128. Another high frequency bypass capacitor 129 is connected between the left-hand terminal of resistor 125and the line 113. The lower terminal of the primary winding of transformer 118, as it appears in the drawing, is connected to the collector of transistor 117. The upper terminal of the primary winding is connected through a capacitor 130 to the base of transistor 117. The transistor 117 and its circuit connections function as an oscillator in a conventional manner, and supply alternating current to the primary winding of transformer 118. Transformer 118 is wound as a step-up transformer, and the high voltage obtained from its secondary winding. Current flows from the secondary winding through the diode 119, which acts as a half-wave rectifier, to a capacitor 131, which smooths the pulses due to the half-wave rectification. A resistor 132 and a voltage regulating diode 133 are connected in series across the capacitor 131. The power supply for the Geiger tubes is taken across the voltage regulating diode 133 through a resistor 134 connected to the anodes of the diodes and a relatively small resistor 135 connected between the cathodes of the diodes and the negative line 113. The resistor 134 may be, for example, 2.2 megohms and the resistor 135 may be 4700 ohms. The provision of this relatively small resistor in the cathode circuits of the Geiger tubes provides a sharply peaked output pulse across that resistor when one of the Geiger tubes breaks down. Such a sharply peaked pulse is illustrated at 136 in FIG. 3 as having a peak potential of 5 volts and a duration of 20 microseconds. The Geiger tubes are self-quenching, being preferably of the halogen quenched type.

The output signal from the Geiger tubes, appearing across resistor 135, is supplied to the input of the monostable multivibrator, whose circuit elements are so chosen that it will respond to a sharply peaked 20 microsecond input pulse by producing a square wave output pulse of about 2 milliseconds duration. The multivibrator circuit illustrated is conventional and any equivalent multivibrator circuit may be used in its place.

The collector of transistor 120 is connected through a resistor 137 to the positive supply line 111. The collector of transistor 120 is also connected to the base of that transistor through the resistor 138. The emitters of both transistors 120 and 121 are connected together and through a resistor 139 to the negative line 113. A diode 144a connects the line 113 to the base of transistor 120, to dissipate any reverse input pulse which may appear across resistor 135.

The collector of transistor 121 is connected to the positive line 111 through a resistor 140 and to the base of transistor 121 through a resistor 141. The base of transistor 121 is also connected through a capacitor 142 to the collector of transistor 120. The output signal of the multivibrator is taken from the collector of transistor 121 and is passed through a coupling capacitor 143 to the integrating circuit consisting of diode 122 and capacitor 123. A diode 144 is connected between negative line 113 and the common terminal of capacitor 143 and diode 122.

In the multivibrator, transistor 120 is normally OFF and the transistor 121 is normally ON. A positive input pulse applied to the base of transistor 120 turns it ON and charges capacitor 142, making its left-hand terminal positive. The charging of capacitor 142 applies a signal between the emitter and base of transistor 121 in a direction effective to cut that transistor OFF, thereby swinging its collector substantially to the potential of line 111 and transmitting a positive-going signal through capacitor 143 and diode 122 to the integrating capacitor 123. Diode 144 serves as a clamp on the signal transmitted through capacitor 143, and prevents that signal from swining negative with respect to line 113. After capacitor 142 is once charged by an input pulse through transistor 120, the transistor 121 remains OFF until the charge on capacitor 142 has dissipated through resistors 140, 141 and 137. The capacitance of capacitor 142 may be made large with respect to the resistance of resistors 137, 140 and 141 to control the timing of the output pulses of the multivibrator, as desired. As shown, the multivibrator is designed to produce an output pulse of 2 milliseconds duration and approximately 8 volts amplitude in response to a single short duration peaked input pulse. Typically, when the Geiger tubes are aligned with a beam of radiation energy, the input pulses will arrive much more often than the 2 milliseconds duration established for the multivibrator output. Consequently, the capacitor 142 will be kept charged and the capacitor 123 will be kept charged. Even if the spacing of the input pulses is somewhat greater than 2 milliseconds, the integrating capacitor 123 holds its charge over a substantially longer interval.

A resistor 145 is connected across the integrating capacitor 123, and is provided With a movable tap, which is connected to the base of transistor 124. The emitter of transistor 124 is connected to negative line 113. The collector of transistor 113 is connected through a load resistor 146 to the detector unit output line 115 and thence to relay 94 and meter 71. A capacitor 147 is conneeted between the wire 115 and the base of transistor 124.

The transistor 124 amplifies the signal appearing across the capacitor 123. The gain is adjusted by moving the tap on resistor 145, to a value such that the relay 94 Will close its contact in response to a signal 150 at the integrating circuit output having an amplitude substantially less than the amplitude of the square wave pulse 151 at the output of the multivibrator. Preferably, the relay 94 should close its contacts in response to a signal 150 having an amplitude about one-tenth that of the multivibrator output signal. In the specific example illustrated, the relay 94 closes its contacts in response to a signal 150 of 0.7 volt which is initiated by a multivibrator output signal 151 of 8.0 volt. Capacitor 147 introduces a certain delay in the output signal, since that capacitor must be charged before the output signal can go up to a potential large enough to energize relay 94. This delay is also useful, since the charge on capacitor 147 holds the relay 94 energized during minor interruptions in the energization of the integrating capacitor 123. During the pushing of the coke from the oven, coke may sometimes pile up ahead of the pusher ram sufliciently to interrupt the beam of radioactive energy. Such interruptions are not of long duration. The capacitor 147 keeps the relay 94 energized and the ram moving during such minor interruptions.

Summarizing the operation of the circuit of FIG. 3, the impingement of the beam of radioactive energy on the Geiger tubes 61 results in energization of relay 94, which in turn energizes relay 92 and (if signal rail 9 is energized) interlocking relay 83. As long as relay 83 is energized, the pusher car operator may actuate the push button 80 to close the motor 79 to drive the pusher in the forward or pushing direction. If the beam of radioactive energy is interrupted for a time determined by the characteristics of the detector circuit, then the relays 94, 92 and 83 are deenergized, effectively stopping the forward movement of the pusher.

The following table shows, by way of example, the identification of specific circuit elements which have been used in a particular embodiment of the invention that has been in successful operation. It should be understood that the invention is not limited to these particular circuit elements, or to any one of them.

Table I Circuit element: Identification Geiger tube 61 Anton type #313. Diodes 101, 102 Type 1N2071. Fuse 103 amp. Resistor 104 3.5K, w. Resistor 105 220K, 0.5 w. Resistor 106 10 ohms, 1 w. Resistor 107 3K, 25 w. Zener diodes 108, 109 Transitron type #SV-9l5. Capacitor 11-4 160 mf. Resistor 116 560K, 0.5 w.

8 Table 1Continued Circuit element: Identification Transistor 117 Type #2N497. Transformer 118 Philco #32-89052. Diode 119 Hughes 1N2382. Transistor 120, 121 Type #2N332. Diode 122 Type #1N2071. Capacitor 123 mf. Transistor 124 Type #2N335. Resistor 125 680 ohms, l w. Resistor 127 22K, 0.5 W. Capacitor 128 0.5 mf., 200 v. D.C. Capacitor 129 1 mf., 35 v. Capacitor 130 .05 mf.

Capacitor 131 .0015 mf., 3 kv. Resistor 132 5.1M, 0.5 w. Diode 133 Anton type #414. Resistor 134 2.2M, 0.5 w. Resistor 135 4700 ohms, 0.5 w. Resistor 137 5.1K, 0.5 W. Resistor 138 27K, 0.5 W. Resistor 139 1K, 0.5 W. Resistor 140 5.1K, 0.5 W. Resistor 141 18K, 0.5 W. Capacitor 142 0.5 Inf.

Capacitor 143 1.5 mf.

Diodes 144, 144a 1N2071.

Resistor 145 25K, 1 W. Resistor 146 270 ohms, 0.5 w. Capacitor 147 10 mf., 35 v.

In the Geiger tube circuit just described, it should be noted that the circuit is arranged to provide a relatively small amplitude (5 volts), short duration (20 microseconds) pulse when one of the Geiger tubes breaks down. This pulse is taken across a relatively low resistance in series with the cathodes of the Geiger tubes. The Geiger tubes are operated at a voltage (10004200 volts) somewhat greater than is conventional, in order that the output pulse across resistor 135 may have amplitude sufiicient to trip the monostable multivibrator. Halogen quenched Geiger tubes are preferable because they are not damaged by operation at these higher voltages. By the use of this short duration output pulse from the Geiger tubes, the resolving time of the Geiger tube system is greatly improved, i.e., shortened, as compared to conventional Geiger tube circuits. This shorter resolving time permits operation of a large number of Geiger tubes in parallel without an appreciable loss in counting accuracy. This is a distinct advantage at high counting rates.

The monostable multivibrator produces a square wave output pulse which does not require additional pulse shaping stages. The circuit constants are chosen to provide a maximum output voltage across the capacitor 123 of the integrating circuit in response to a relatively small number of pulses generated by the Geiger tube. This is accomplished by adjusting the ON time of the monostable multivibrator to make its output pulses long as compared with the short duration input pulses. After this relatively small threshold pulse rate is reached, further increases in the incident radiation do not result in any changes in the integrator output potential. By virtue of this arrangement, the circuit provides an output control potential to the relay 94 which is substantially constant and nearly independent of many variable factors such as reduced radiation due to decay of the source or minor obstructions in the oven. This makes the apparatus very stable and eliminates the need for sensitivity adjustments.

The arrangement just described is of particular advantage in any situation Where it is desired to have Geiger tubes turn a circuit on in response to the presence of radioactive rays and turn it off in the absence of those rays. Such an on-ofi": control in response to the presence or absence of radioactive rays is useful in many different control problems.

While We have shown and described a preferred embodiment of our invention, other modifications will readily occur to those skilled in the art, and we therefore intend our invention to be limited only by the appended claims.

What is claimed is: V

1. Apparatus for detecting radioactive rays, comprismg:

(a) a first casing adapted for mounting on a wall;

(b) a second casing attached to the first casing;

(c) at least one Geiger tube inside the second casing;

(d) signal means in said first casing;

(e) circuit means controlled by the Geiger tube for actuating the signal means;

(f) circuit elements in said circuit means;

wherein the improvement comprises:

(g) a frame located outside said first casing and supporting said circuit elements and the Geiger tube;

(h) electrical connector means in said circuit means including a plug component and a jack component, one of said components being fixed to said frame and the other being fixed to an outside Wall of the first casing and accessible from the exterior thereof, said electrical connector means providing the only support for said frame;

(i) said second casing being cylindrical, closed at one end and open at the other end and enclosing said frame and the Geiger tube and circuit elements supported thereon; and

(j) means including a collar having a freely rotatable connection with the open end of said second casing and a threaded connection With the first casing, said collar being concentric :With the plug and jack;

(k) so that said frame, and the Geiger tube and circuit elements supported thereon may be disconnected from said first casing by removing said collar and said second casing and separating the plug and jack components of the electrical connector means.

2. Detector apparatus as defined in claim 1, in which said frame is of generally cylindrical contour and includes a pair of end disks connected by a plurality of elongated through bolts, said plug being located centrally in the end disk at the open end of the second casing.

3. Apparatus for indicating the presence of a beam of radioactive rays, comprising:

(a) at least one Geiger tube;

(b) circuit means including the tube and having an output and efiective to produce at its output a shapely peaked pulse each time a ray impinges on the Geiger tube;

(c) a monostable multivibrator having an input and an output;

(d) means connecting the output of the circuit means to the multivibrator input;

(e) said multivibrator being effective to produce at its output a square Wave pulse of fixed duration and amplitude in response to each peaked pulse at its input;

(f) an integrating circuit having an input and an output; and

(g) means connecting the output of the multivibrator to the input of the integrating circuit;

wherein the improvement comprises:

(h) indicator means shiftable between only two distinct conditions respectively indicative of the presence and absence of a beam of rays;

(i) amplifier means having an input connected to the output of the integrating circuit and an output operatively connected to the indicator means;

(1') said amplifier means being effective to drive the indicator means to its beam presence indicating condition in response to an electrical signal at the integrating circuit output having an amplitude substantially less than the amplitude of the square wave pulse at the output of the multivibrator.

4. Apparatus as defined in claim 3, in which said amplifier means is eifective to drive the indicator means to its beam presence indicating condition in response to a signal at the integrating circuit output equal to about one-tenth of the multivibrator output square wave amplitude.

References Cited UNITED STATES PATENTS 2,752,508 6/1956 Zito 25083.6 2,822,479 2/1958 Goldsworthy 250-83.6 X 2,960,607 11/1960 Kohl 25083.6 X 2,974,231 3/1961 Greenblatt et al. 25083.6 X

ARCHIE R. BORCHELT, Primary Examiner.

U.S. Cl. X.R. 250-83 J3 

